This invention lies in the field of systems for burning fuel oil. More particularly, it concerns apparatus for atomizing the fuel oil in preparation for discharge into the flame zone in the combustion chamber. Still more particularly, it concerns the design of a liquid fuel atomizer which will provide particles of liquid fuel of the least possible size for rapid evaporation and combustion, with good flame characteristics.
Systems long have been known for atomization of oil in immediate preparation for its burning as fuel. However, the term "atomization" is a gross misnomer since the liquid oil is not, literally, broken-up into its component atoms, but is caused to be broken up into micron-size particles which are small enough for instant vaporization or conversion from liquid to the gaseous state in the flame. Oil, to burn, must be in the gaseous state in order to mix with air for burning, in a series of heat-productive oxidation chemical reactions. The oil, a hydrocarbon, is through oxidation converted to carbon dioxide and water vapor, at a very high temperature in the flame.
There are two generic systems for atomization of oil, on which there are myriad variations which are well-known to those versed in the art. One system known as the "outside-mix" was initially used at the expense of great steam consumption for atomization. A second system quickly came into being for steam conservation. It is called the "inside-mix". Nomenclature denotes the point at which oil and steam are mixed in preparation for atomization. There is little cause for speculation as to how the typical "outside-mix" atomizer functions, and atomization is attributed to the `shearing` action of steam on oil. Over the years, there has been considerable academic discussion as to why the `inside-mix` atomizer reduces steam demand; also as to how it functions. One school holds that the pressurized steam-oil mixture greatly enchances high-energy steam-oil contact for better `shearing` action. Another school holds that the pressurized steam-oil contact creates a high-pressure steam and oil bubbly emulsion which, upon reaching atmospheric pressure, explodes to form the required micron-size droplets.
The "how-and-why" discussion is academic because the inside-mix burners require only a small fraction of the atomizing steam for a specific heat release, that would be required for outside-mix operation. But there is significant variation in steam demand for atomization as between different inside-mix oil atomizers. Desperately needed steam conservation measures prompt research toward minimization of steam for atomization, in view of the current energy situation.
The excellence of any atomizer, at any steam consumption rate, is based on the quality of oil flame it produces. That is, if reduction in steam quantity results in an intolerable flame condition, there is no solution toward steam demand reduction, and all atomizers must be judged as at a minimal steam consumption basis for comparison. Steam consumption measurement is taken as "pounds of steam per pound of oil". Each pound of #6 (bunker C) oil when completely burned produces a heat release (lower heating value) of very close to 17,500 btu. Lowest practical heat release per atomizer is 2,000,000 btu/hr and the maximum may be as great as 200,000,000 or even more. Demand for atomizing steam on a pound-per-pound basis increases as heat release per atomizer decreases and the steam requirement decreases as the heat release per atomizer increases. Thus, it is common to use 8,000,000 btu/hr heat release for checking atomizer steam demand. On this basis, the atomizer design of this invention requires less steam than any other design for production of a satisfactory flame.